Zirconium dioxide-based electrode-electrolyte pair (variants), method for the production thereof (variants) and organogel

ABSTRACT

This invention relates to the field of electric power generation by direct transformation of the chemical energy of gaseous fuel to electric power by means of high-temperature solid oxide fuel cells. The invention can be used for the fabrication of miniaturized thin filmed oxygen sensors, in electrochemical devices for oxygen extraction from air and in catalytic electrochemical devices for waste gas cleaning or hydrocarbon fuels conversion. The technical objective of the invention is the production of a low-cost electrode-electrolyte pair having an elevated electrochemical efficiency as the most important structural part of a highly efficient, economically advantageous and durable fuel cell. Furthermore, the invention achieves additional objectives. The achievement of these objectives is exemplified with two electrode-electrolyte pair designs and their fabrication methods, including with the use of a special organogel.

TECHNICAL FIELD

This invention relates to the field of electric power generation bydirect transformation of the chemical energy of gaseous fuel to electricpower by means of high-temperature solid oxide fuel cells.

Additionally, the invention can be used for the fabrication ofminiaturized thin filmed oxygen sensors, in electrochemical devices foroxygen extraction from air and in catalytic electrochemical devices forwaste gas cleaning or hydrocarbon fuel conversion.

STATE OF THE ART

In the recent years, major attempt has been made world over aimed at thedevelopment of high-temperature oxide fuel cells that act as uniquedevices for the generation of electric power from natural or syntheticgaseous fuels.

A high-temperature fuel cell consists of two porous electrodes having anelectronic conductivity type and a dense electrolyte in the spacebetween them having an ionic conductivity type. The gaseous fuel islocated at the side of one of the electrodes. The oxidizing agent,typically air, is located at the side of the other electrode.

The most important component of the oxide fuel cell structure thatdetermines the efficiency of electric current generation is theelectrode-electrolyte pair. The electrolyte of the fuel cell istypically doped zirconium dioxide which has a good high temperatureconductivity of oxygen ions.

The following electrode-electrolyte pairs are known.

Known is an electrode-electrolyte pair wherein, aiming at reducing itselectrical resistivity, an electrolyte is used on the basis ofscandium-stabilized zirconium dioxide and a sublayer between the cathodeand the electrolyte consisting of yttrium- and terbium-doped zirconiumdioxide having an electronic conductivity type (U.S. Pat. No. 6,207,311A, published 2001).

However, this electrode-electrolyte pair does not achieve the objectiveof increasing the area of electrochemical contact in the pair anddecreasing the electrolyte layer thickness and the negative effect ofthe surface stress concentrators that cause crack initiation in theelectrolyte layer. Further disadvantage of this electrode-electrolytepair is the high cost of terbium.

In another high-temperature fuel cell (U.S. Pat. No. 5,518,830 A,published 1996), aiming at reducing the electrical resistivity of itselectrode-electrolyte pair, an electrolyte is used on the basis ofyttrium-stabilized zirconium dioxide and a sublayer between the cathodeand the electrolyte consisting of yttrium- and terbium-doped zirconiumdioxide having a p-type of electronic conductivity. Aiming at reducingthe electrical resistivity of another electrode-electrolyte pair, anelectrolyte is suggested on the basis of yttrium-stabilized zirconiumdioxide and a sublayer between the cathode and the electrolyteconsisting of titanium-doped zirconium dioxide having an n-type ofelectronic conductivity.

Disadvantages of said structure are as mentioned for the case above.

Known also is a solid oxide fuel cell with a cathodic and an anodicelectrode-electrolyte pairs (RU 2128384 A, published Mar. 27, 1999, cl.H 01 M 8/10). The solid electrolyte of the element based on metal-dopedzirconium dioxide contacts with the electrode by smoothinterpenetration.

Disadvantage of these pairs is the limited area of electrochemicalcontact at the anodic and the cathodic sides which limits the currentgeneration efficiency of the fuel cell.

Known also are a cathode-electrolyte pair based on yttrium-dopedzirconium dioxide and an anode-electrolyte pair based on yttrium-dopedzirconium dioxide with a separating buffer sublayer consisting of afine-grained mixture of powdered electrolyte and cathode materials and afine-grained mixture of powdered electrolyte and anode materials,respectively (U.S. Pat. No. 5,935,727 A, published 1999).

Said structure achieves an increase in the electrode and electrolytecontact area.

However, the fabrication of said pair which requires powder sintering at1350° C. unavoidably leads to chemical interaction between the cathodeand anode materials, on the one hand, and the electrolyte material, onthe other. This interaction results in an increase in the electricalresistivity of the electrolyte to electrode contacts and produces a highlevel of mechanical stresses in the electrolyte layer that may initiatecracking therein.

Further disadvantage of the above described devices is that theelectrolyte of the electrode-electrolyte pair is mainly in the form of atwo-dimensional layer on the surface of the porous electrode. Thisunavoidably results in mechanical stresses due to the roughness-relatedstress concentrators on the surface of the porous electrode beingdirected across the electrolyte layer thus drastically increasing theprobability of cracking therein. Furthermore, the thinner theelectrolyte, the higher the cracking probability.

The following electrode-electrolyte pair fabrication methods are known.

Known is an electrode-electrolyte pair fabrication method by depositinga coating containing water solutions with a polymerizing organic solvent(U.S. Pat. No. 5,494,700 A, published 1996) comprising the steps of:

-   -   producing a water solution of zirconium and yttrium nitrates,        chlorides or carbonates;    -   mixing said water solution with ethylene glycol to act as a        polymerizing agent;    -   adding nitric, hydrochloric, citric or oxalic acid for solution        pH optimization;    -   heating said mixture to 25-100° C. for polymerization and        viscosity optimization;    -   depositing said mixture onto the surface of the porous        electrode;    -   drying the deposited mixture at about 300° C.;    -   high temperature annealing for removal of all the impurities and        crystallization of the yttrium-doped zirconium dioxide.

Disadvantages of this method are the strong dependence of the propertiesof the thus obtained electrolyte layer on the initial mixturepolymerization degree and viscosity; poor adhesion to the electrodematerial; high content of impurities that impair the electrochemicalproperties of the electrolyte and the electrode-electrolyte pair; poorreproducibility of the method due to the complex chemical processes usedfor the production of the polymer solution; insufficient adaptability ofthe method with respect to the choice of electrolyte composition and thematerial and properties of the electrode.

Known also is an electrode-electrolyte pair fabrication methodcomprising depositing an organogel coating consisting of fine-grainedparticles of yttrium-doped zirconium dioxide in an organic liquid (U.S.Pat. No. 5,968,673 A, published 1999) comprising the steps of:

-   producing the organogel consisting of 0.2-0.4 μm yttrium-doped    zirconium dioxide powder (4 wt. parts) and an organic liquid (100    wt. parts) consisting of ethyl alcohol, a dispersant    (alkylpolyoxyethylene phosphorus ether), a binder (ethylcellulose),    an anti-foaming agent (sorbitanoleate) and a volatile solvent;-   depositing the organogel onto the electrode surface;-   drying at 100° C. for 1 h;-   annealing at 1500° C. for 5 h.

In fact, the formation of the electrolyte layer on the electrode occursin this case due to electrolyte material powder sintering. Therefore themain disadvantages of said method are the high power consumption of thetechnological process and the poor electrochemical properties of theelectrolyte and the electrode-electrolyte pair.

Known is an organogel consisting of 0.2-0.4 μm yttrium-doped zirconiumdioxide powder (4 wt. parts) and an organic liquid (100 wt. parts)consisting of ethyl alcohol, a dispersant (alkylpolyoxyethylenephosphorus ether), a binder (ethylcellulose), an anti-foaming agent(aorbitanoleate) and a volatile solvent (U.S. Pat. No. 5,968,673 A,published 1999).

Disadvantages of said organogel are that it does not contribute to theformation of the dense structure in the electrolyte, does not favortemperature reduction, does not provide any applicable choice ofelectrode materials based on zirconium dioxide and does not provide fora technologically suitable method of electrolyte production onelectrodes having different properties and parameters.

DISCLOSURE OF THE INVENTION

The technical objective of the invention is the production of a low-costelectrode-electrolyte pair having an elevated electrochemical efficiencyas the most important structural part of a highly efficient,economically advantageous and durable fuel cell.

Each of the inventions included into the group is aimed at achieving aseparate additional objective.

More particularly, the electrode-electrolyte pair embodiment shown asthe first and the fourth objectives of the invention in the suggestedgroup of inventions achieve additional technical objectives comprising:

-   reduction of the working temperature of the electrochemical device    comprising the electrode-electrolyte pair;-   increasing the operation efficiency and reliability of the    electrode-electrolyte pair;-   reduction of the dimensions and weight per unit power generated by    the fuel cell comprising the electrode-electrolyte pair;-   adaptability of the design, materials and dimensions of the    electrode;-   higher adaptability of the electrode-electrolyte pair and lower    thickness of the electrolyte layer.

Furthermore, the electrode-electrolyte pair fabrication methods shown asthe second and fifth objectives of the invention in the suggested groupof inventions achieve additional technical objectives comprisingincreasing the technological suitability of the method for commercialfabrication of the electrode-electrolyte pair, increasing thefabrication efficiency and reduction of the cost of theelectrode-electrolyte pair and the entire electrochemical device,reduction of power consumption and increasing the adaptability of themethod.

Furthermore, the organogel comprised in the components used for thefabrication of the first embodiment of the electrode-electrolyte pairand shown as the third objective of the invention in the suggested groupof inventions achieves additional technical objectives comprisingreducing the cost of the organogel, increasing its adaptability,increasing its adhesion to the electrode material and avoidingelectrolyte contamination with detrimental impurities.

Below, embodiments of the electrode-electrolyte pair design,electrode-electrolyte pair fabrication methods and materials used aredisclosed in accordance with the invention claimed herein that achievesaid technical objective.

The first embodiment of the electrode-electrolyte pair comprises amicroporous electrode to the surface of which is deposited amultilayered solid electrolyte based on zirconium dioxide withstabilizing additions. The solid electrolyte consists of the innernanoporous three-dimensional solid electrolyte layer. The grain size ofthis electrolyte layer is within 1000 nm. The inner layer fills, atleast partially, the surface pores of the microporous electrode to adepth of 5-50 μm. On the surface of the inner layer there is a denseouter electrode layer. The grain size of this electrolyte layer is alsowithin 1000 nm.

The inner and outer electrolyte layers may have similar or differentcompositions.

The inner electrolyte layer has a combined amorphous and nanocrystallinestructure.

The outer electrolyte layer has an amorphous structure.

As the stabilizing additions, the first electrolyte contains magnesiumand/or calcium and/or yttrium and/or scandium and/or aluminum and/orrare earth metals and/or titanium.

The electrode is in a microporous ceramic or metallic or metalloceramicmaterial with pore sizes of above 1 μm.

The electrode of the pair is anode or cathode with a flat or pipe-likeshape.

The anode is in a porous metallic material consisting of nickel and/orcobalt and/or their alloys.

The anode is made of a volume mesh or a foam material.

The electrolytic efficiency of the electrode-electrolyte pair and theentire electrochemical device is increased due to the followingadvantages:

-   increasing the lateral conductivity of the electrolyte due to the    optimization of the outer and inner zirconium dioxide layers by    doping;-   increasing the electric contact area of the electrolyte with the    electrode material due to the use of the inner surface of electrode    pores;-   reduction of the electrical resistivity at the electrode-electrolyte    boundary due to the low electrode deposition temperatures;-   increasing the electrochemical contact area of the gaseous phase,    the electrode and the electrolyte due to the nanoporous inner    electrolyte layer and the surface conductivity.

Reduction of the working temperature of the electrochemical deviceconsisting of the electrode-electrolyte pair is achieved due to theabove advantages and the possibility of producing a dense electrolytelayer having a minimum thickness.

Increasing the operation efficiency and reliability of theelectrode-electrolyte pair is achieved due to the high strength of theamorphous and nanocrystalline structure of zirconium dioxide;elimination of the surface stress concentrators in the electrode due tothe nanoporous inner electrode layer; the high damping capacity of theinner nanoporous and the three-dimensional electrolyte layers that avoidcracking in the electrolyte.

As is well known, the cost, dimensions and weight of an electrochemicalgenerator consisting of fuel cells are determined as per unit generatedpower. Therefore any increase in the electrochemical efficiency of theelectrode-electrolyte pair reduces the cost, dimensions and weight. Forexample, in the generation of 1 kW of electric power, an increase in theunit power from 0.25 W/cm² to 1 W/cm² results in a 4-fold costreduction, decrease in the dimensions, i.e. fuel cell area, from 0.4 m²to 0.1 m² and a 4-fold weight reduction.

The increase in the adaptability of the device technology is achieveddue to the possibility of using electrodes having a porosity of above 1μm made from ceramic, metalloceramic and metallic materials, in the formof a cathode or anode having a flat or pipe shape.

The electrode-electrolyte pair fabrication method based on zirconiumdioxide following the first embodiment of the invention comprises theformation, on the microporous electrode surface, of a partiallyelectrode-penetrating multilayered solid electrolyte based on zirconiumdioxide with stabilizing additions. During the formation, themicroporous electrode surface is initially impregnated with organogelconsisting of particles of zirconium dioxide with stabilizing additionsand an organic solution containing organic salts of zirconium and thestabilizing metals. The next step is destruction of the organogelorganic part that leads to the chemical deposition of the innernanoporous three-dimensional solid electrolyte layer on the electrodesurface. Then, the inner organogel layer is deposited onto the surface,said layer consisting of nanosized particles of zirconium dioxide withstabilizing additions and an organic solution containing organic saltsof zirconium and the stabilizing metals. The next step is destruction ofthe organogel organic part that leads to the chemical deposition of thedense outer layer of the multilayered electrolyte onto the inner layersurface.

The organogel used for the formation of the inner and outer solidelectrolyte layers can be of similar or different compositions.

The stabilizing additions for the solid electrolyte according to thismethod can be magnesium and/or calcium and/or yttrium and/or scandiumand/or aluminum and/or rare earth metals and/or titanium.

The microporous electrode surface is impregnated with organogel invacuum or by mechanical pressing the organogel into the microporoussurface of the electrode.

Destruction is performed by high-energy impact that causes thedescomposition of the organic part of the organogel, e.g. thermal,induction or infrared heating, or electron or laser beam impact orplasmachemical impact.

Organogel destruction is performed with high-rate pyrolysis attemperatures within 800° C. in an oxidizing, inert or weakly reducinggas atmosphere.

Organogel organic part destruction is performed simultaneously or insequence, by organogel impregnation or deposition to the inner layersurface.

During organogel impregnation of the electrode or organogel depositionto the inner layer surface with simultaneous destruction, the organogelis deposited to the surface to be coated by spraying or printing.

During organogel impregnation of the electrode or organogel depositionto the inner layer surface with subsequent destruction, the organogel isdeposited to the cold surface of the electrode or the inner layer withsubsequent high-rate heating of the electrode.

Organogel impregnation of the electrode or organogel deposition to theinner layer surface and organogel destruction are performed in one ormultiple steps.

Said technical result is achieved due to the high rate of materialdeposition and electrolyte formation on the electrode surface;possibility of using simple and cheap equipment, use of lowtemperatures, possibility of setting up the technological process in acompletely automatic conveyor embodiment; method adaptability withrespect to electrolyte composition choice; method adaptability withrespect to electrode-electrolyte pair design choice; possibility oftaking the properties and parameters of the electrode materials intoaccount.

The organogel used for the fabrication of the electrode-electrolyte paircontains nanosized particles of zirconium dioxide with stabilizingadditions and an organic solution containing organic salts of zirconiumand the stabilizing metals, a mixture of α-branching carbonic acids withthe general formula H(CH₂—CH₂)_(n)CR′R″—COOH, where R′ is CH₃, R″ isC_(m)H_((m+1)) and m is from 2 to 6, with an average molecular weight of140-250.

The stabilizing metals used for the organogel are magnesium and/orcalcium and/or yttrium and/or scandium and/or aluminum and/or rare earthmetals and/or titanium.

As the organic solvent, the organogel contains carbonic acid and/or anyorganic solvent of carbonic acid metal salts.

The organogel contains nanosized particles from 3 to 100 nm.

The concentration of stabilizing additions in zirconium and metal saltsin the organogel is selected at 0.05 to 1 mole/l in a ratiocorresponding to the electrolyte stoichiometric composition.

The volume ratio of the nanosized particles in the organogel is within85%.

The second embodiment of the electrode-electrolyte pair comprises ananoporous electrode to the surface of which is deposited a layer ordense three-dimensioned electrolyte based on zirconium dioxide withstabilizing additions the grain size of which is within 1000 nm. Theelectrolyte fills the surface pores of the nanoporous electrode to adepth of 1-5 μm.

The electrolyte has an amorphous structure.

As the stabilizing additions, the electrode-electrolyte pair containsmagnesium and/or calcium and/or yttrium and/or scandium and/or aluminumand/or rare earth metals and/or titanium.

The electrode is in a microporous ceramic or metallic or metalloceramicmaterial with pore sizes, at least near the surface, of within 1 μm. Inthis embodiment of the electrode-electrolyte pair, the electrode mayhave a functional or technological sublayer on the surface. Thissublayer can be in a nanoporous cathodic or anodic material, anotherelectrolyte material or a fine-grained mixture of the electrode and theelectrolyte materials.

The electrode of the pair is anode or cathode with a flat or pipe shape.

The anode is in a porous metallic material consisting of nickel and/orcobalt and/or their alloys.

The electrode-electrolyte pair fabrication method based on zirconiumdioxide following the second embodiment of the invention comprises theformation, on the microporous electrode surface, of a densethree-dimensional solid electrolyte layer based on zirconium dioxidewith stabilizing additions. During the formation, the nanoporouselectrode surface is initially impregnated with an organic solutioncontaining organic salts of zirconium and the stabilizing metals, amixture of α-branching carbonic acids with the general formulaH(CH₂—CH₂)_(n)CR′R″—COOH, where R′ is CH₃, R″ is C_(m)H_((m+1)) and m isfrom 2 to 6, with an average molecular weight of 140-250. The next stepis destruction of the solution organic part that leads to the chemicaldeposition of the solid electrolyte on the electrode surface.

As the stabilizing additions, the electrode-electrolyte pair containsmagnesium and/or calcium and/or yttrium and/or scandium and/or aluminumand/or rare earth metals and/or titanium.

As the organic solvent, the solution contains carbonic acid or tolueneor octanol or any organic solvent of carbonic acid metal salts.

Destruction is performed by high-energy impact that causes thedecomposition of the organic part of the solution, e.g. thermal,induction or infrared heating, or electron or laser beam impact orplasmachemical impact.

Solution destruction is performed with high-rate pyrolysis attemperatures within 800° C. in an oxidizing, inert or weakly reducinggas atmosphere.

Solution organic part destruction is performed simultaneously or insequence with the impregnation.

During electrode impregnation with simultaneous destruction, thesolution is deposited to the surface to be coated by spraying orprinting.

During electrode impregnation with subsequent destruction, the solutionis deposited to the cold surface of the electrode with subsequenthigh-rate heating of the electrode.

The concentration of stabilizing additions in zirconium and metal saltsin the solution is selected at 0.05 to 1 mole/l in a ratio correspondingto the electrolyte stoichiometric composition.

Solution deposition onto the electrode or destruction are performed inone or multiple steps.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows schematic of one embodiment of the electrode-electrolytepair according to the invention.

FIG. 2 shows schematic of another embodiment of theelectrode-electrolyte pair.

EMBODIMENTS OF THE INVENTION

The electrode-electrolyte pair (FIG. 1) comprises a microporouselectrode 1 with pores 2, an inner nanoporous three-dimensional solidelectrolyte layer 3 and a dense outer solid electrolyte layer 4. FIG. 2shows a nanoporous electrode 2 with pores 6 and a densethree-dimensional solid electrolyte layer 7.

The efficiency of a fuel cell (electrical power generated per unitsurface) is determined by the following factors:

-   ionic conductivity of the electrolyte based on zirconium dioxide    (the higher the conductivity, the greater the power available);-   electrolyte layer thickness (the greater the thickness, the greater    the power);-   electrical resistivity at the electrode-electrolyte boundary (the    lower the resistivity, the greater the power);-   contact area between the electrode and the electrolyte (the greater    the area, the greater the power);-   electrochemical contact area of the gaseous phase, the electrode and    the electrolyte (the greater the electrochemical contact area, the    greater the power).

Thus, the efficiency of a fuel cell, i.e. that of anelectrode-electrolyte pair, is determined by the composition ofzirconium dioxide and the electrode-electrolyte pair design.

The operation efficiency of the electrode-electrolyte pair is mainlydetermined by the density of the zirconium dioxide electrolyte layer(absence of through pores and macrocracks) and its ability to resistthermal stresses both during the fabrication and during the operation ofthe fuel cell. The latter quality of the electrolyte layer materialdepends on the strength of the material, electrolyte adhesion to theelectrode material and the ability of the electrode-electrolyte pair torelieve mechanical stresses without forming cracks, taking into accountthe role of the surface stress concentrators on theelectrode-electrolyte boundary.

Thus, the efficiency of the electrode-electrolyte pair, is determined bythe composition of metal-doped zirconium dioxide, its mechanicalproperties under the condition of their maximum matching with themechanical properties of the electrode and the design of the zirconiumdioxide layer on the porous electrode surface.

The possibility of achieving the optimum properties and parameters of anelectrode-electrolyte pair is determined by its fabrication method.

As the electrolyte material for fuel cells, metal-doped zirconiumdioxide is used. As the doping metals, alkaline and rare-earth metals,yttrium, scandium, aluminum and titanium are used. Doping allowsproducing partially stabilized zirconium dioxide (tetragonal structure)or completely stabilized zirconium dioxide (cubic fluorite structure).Tetragonal zirconium dioxide has a higher strength as compared with thecubic one but lower oxygen ion conductivity. Moreover, doping allowsproducing zirconium dioxide of combined conductivity that can be used asa sublayer on the cathode or anode for reducing the electricalresistivity at the electrode-electrolyte boundary.

According to this embodiment of the invention (FIG. 1) electrode 1 canhave a flat or pipe shape, act as a cathode or an anode and be made froma ceramic, metallic or metalloceramic material with a pore size of above1 μm. For example, anode can be made from metals, such as nickel, cobaltor their alloys; metalloceramics, such as NiO(Ni)-stabilized zirconiumdioxide, NiO(Ni)-stabilized cerium dioxide, CoO(Co)-stabilized zirconiumdioxide or CoO(Co)-stabilized cerium dioxide. A metallic anode can bemade from foam metal or a volume mesh. Ceramic cathode can be made fromperovskite family ceramics, such as LaMnO₃, LaCoO₃, LaNiO₃, lanthanumgallates and other metal oxides having a good electronic conductivityand catalytic activity to ionize air oxygen. Cathode can be made frommetal with a protective oxide coating. Electrode porosity is typically20 to 80%.

The inner nanoporous three-dimensional layer 3 consisting of stabilizedzirconium dioxide penetrates into the porous electrode 1 to a depth of5-50 μm. The stabilizing metals can be calcium, magnesium, yttrium,scandium, aluminum, rare-earth and transition metals and titanium. Thepenetration depth (H) depends on electrode pore diameter (D), typicallyas H=(2-3) D.

The key problem of thin electrolyte layer efficiency and reliability,however produced, is its defectiveness, i.e. the presence of pores andmicrocracks, as well as poor adhesion. The main origin of this problemare the high thermal and internal stresses both in the electrolyteitself and on the phase boundary. During electrode deposition onto theporous surface of electrode 1, the surface microroughnesses act asstress concentrators thus leading to crack initiation even at relativelylow thermal and internal stresses.

In the invention disclosed herein, of extreme importance is the innernanoporous three-dimensional electrolyte layer 3 made from stabilizedzirconium dioxide. For example, due to the penetration of the layer 3into the electrode 1, its nanoporousity and the good adhesion to thematerials of the electrode 1, the surface stress concentrators areeliminated, the electrode and electrolyte thermal expansion coefficientsare matched and the mechanical stresses are relieved. The above effectsbecome even stronger if the inner layer 3 has a porosity gradient, i.e.an increase in porosity from the electrode surface downwards. Thesefactors tangibly increase the reliability and operation efficiency ofthe electrode-electrolyte pair, primarily expressed in the prevention ofcracking and defect formation in the dense layer 4. Moreover, thisadvantage provides for the minimization of the thickness of the denselayer 4, thus reducing the working temperature of the electrochemicaldevice and an increase in its electrochemical efficiency.

For example, the suggested inner layer 3 consisting of tetragonalzirconium dioxide can relieve stresses of up to 1000 MPa when incombination with a ceramic electrode and up to 2000 MPa when incombination with a metallic electrode. By way of comparison, thecritical stress for a dense two-dimensional layer 4 of tetragonalzirconium dioxide is 400-450 MPa.

The suggested inner layer 3 consisting of cubic fluorite zirconiumdioxide can relieve stresses of 30-40% lower than tetragonal zirconiumdioxide can. By way of comparison, the critical stress for a densetwo-dimensional layer 4 of cubic zirconium dioxide is 180-250 MPa.

The high strength and cracking resistance of the inner layer 3 that areof primary importance for the fabrication of the electrode-electrolytepair are achieved due to the three dimensions and the specific combinedstructure consisting of 3-1000 nm grains and an amorphous phase.

In the invention disclosed herein, the role of the inner nanoporousthree-dimensional layer 3 consisting of stabilized zirconium dioxide isimportant also from the viewpoint of increasing the electrochemicalefficiency of the electrode-electrolyte pair. First, this is due to themultiple increase in the area of the electrical contact between thematerial of layer 3 and the material of electrode 1. Second, thenanocrystalline layer 3 has a higher conductivity of oxygen ions. Forexample, the oxygen ion conductivity of a nanocrystalline layer (grainsize 4-50 nm) of ZrO₂-8% Y₂O₃ electrolyte at 900° C. is 0.05-0.07 Sm/cm,whereas the conductivity of the same electrolyte with a microcrystallinestructure is 0.02-0.03 Sm/cm. Third, the nanoporous layer 3 has a highsurface ionic and electronic conductivity, especially in a wet gaseousatmosphere at the side of the electrode 1. Fourth, doping of stabilizedzirconium dioxide that composes the inner layer 3, e.g. with rare-earthmetals, titanium and transition metals produces a combined type ofconductivity in the layer 3 thereby multiply increasing the area of theelectrochemical contact between the ionic conductor, the electronicconductor and air oxygen (for cathodic electrode) or the fuel (foranodic electrode).

Thus, the inner layer 3 provides for a high current density, a low levelof electrode overstressing and a high specific power of the fuel cell asa whole.

The dense layer 4 of solid electrolyte is a thin two-dimensional layerconsisting of tetragonal or cubic zirconium dioxide that has a 100%ionic type of conductivity. Stabilizing metals can be calcium,magnesium, yttrium, scandium and aluminum. Due to the layer 4localization on the surface of the inner nanoporous layer 3 thateliminates the surface stress concentrators and relieves all thetechnological and thermal stresses, it may be up to 0.5-5 μm inthickness. Due to this fact, the ohmic stresses in the electrolyte areminor, providing for a high electrochemical efficiency of theelectrolyte as is. The amorphous structure of the layer 4 provides forits strength and elasticity that are important at theelectrode-electrolyte pair fabrication stage where the reject percentageis known to be the highest. This advantage indirectly reduces the costof the electrode-electrolyte pair and the electrochemical device as awhole. After the deposition of the electrolyte layer 4 the amorphousstructure of zirconium dioxide can be crystallized without the risk ofcracking in the layer.

The compositions of the layers 3 and 4 can be similar or different. Thecomposition and properties may exhibit a gradient behavior across thelayers 3 and 4. This can be achieved by sequential deposition of thelayers 3 and 4 with an appropriate change in the technologicalconditions and the materials used. This feature broadens the potentialcapabilities of the pair and its technology. Moreover, where one of theelectrolyte layers should have special properties, zirconium dioxide canbe doped with multiple different metals. For example, stabilization oftetragonal zirconium dioxide by scandium and aluminum doping increasesthe strength of the electrolyte as compared with the ZrO₂-3 mole % Y₂O₃composition. Stabilization of tetragonal zirconium dioxide by scandiumand bismuth doping increases the density and ionic conductivity of theelectrolyte as compared with the bismuth free composition.

In the electrode-electrolyte pair embodiment (FIG. 2), the electrode 5can have flat or pipe shape, act as a cathode or an anode and be inceramic, metallic or metalloceramic materials. A currently generallyused embodiment of the electrode 5 is a cathode with a cathodic orelectrolyte sublayer or an anode with an anodic or electrolyte sublayer.

The pores 6 of the electrode or the sublayer are less than 1 μm in size.

The dense three-dimensional dense electrolyte layer 7 consisting ofstabilized zirconium dioxide is located on the electrode surface andpartially penetrates into the pores 6 to a depth of 1-5 μm. The denseelectrolyte layer 7 is tetragonal or cubic zirconium dioxide stabilizedwith metals of the following group: calcium, magnesium, yttrium,aluminum, scandium etc. The layer 7 has an amorphous structure, at leastat the deposition stage. This layer has the same functions and the sameadvantages as the double layer according to the first embodiment of theelectrode-electrolyte pair, the only difference being in that for anelectrode pore size of less than 1 μm there is no need to deposit ananoporous inner electrolyte layer.

The first embodiment of the electrode-electrolyte pair suggested anddisclosed herein (FIG. 1) is fabricated using the first suggestedfabrication method and the suggested organogel.

The organogel is a metalorganic liquid consisting of an organic solutionof zirconium and alloying metal organic salts with an addition ofnanosize particles of stabilized zirconium dioxide. The organic basis ofthe metal salts is a mixture of α-branching carbonic acids with thegeneral formula H(CH₂—CH₂)_(n)CR′R″—COOH, where R′ is CH₃, R″ isC_(m)H_((m+1)) and m is from 2 to 6, with an average molecular weight of140-250. The organic salt solvent is carbonic acid and/or any otherorganic solvent of carbonic acids, e.g. toluene, octanol etc. The mainfunction of the solvent is to adjust the viscosity of the organogel.

The salts of zirconium and alloying metals, such as calcium, magnesium,yttrium, scandium, aluminum, titanium, bismuth, rare-earth metals, e.g.terbium or cerium, and iron group metals, are obtained by extractionfrom water solutions of appropriate metal salts to a mixture of carbonicacids, following which the metal carboxylates are mixed in theproportion as is required for the production of the final electrolytestoichiometric composition. The concentration of each metallic elementin the carboxylates may vary from 0.05 to 1.0 mole/l.

The material of the nanosized particles is stabilized and/or dopedzirconium dioxide. The size of the nanoparticles corresponding to theelectrolyte composition or part of the electrolyte composition is 3 to100 nm. The volume ratio of the particles in the organogel may reach 85%of the total organic liquid volume. The volume ratio of the particles inthe organogel controls the organogel viscosity and the density of theelectrolyte layer deposited. The higher the particles content, thehigher the organogel viscosity and the nanoporosity of the electrolytelayer deposited. The rule for determining the optimum volume ratio ofthe particles in the organogel is as follows: the greater the electrodepore size, the greater the volume ratio of the particles. Organogel isproduced by mechanically mixing the particles and the organic liquid.

The electrolyte layer production method is based on destruction(decomposition) of the organogel organic component deposited on theelectrode surface. An oxide layer forms on the surface, composed of theparticles and oxides of the metals chemically deposited from appropriatemetal carboxylates in the organogel composition. Oxides of metalsdeposited from carboxylates cement the particles between themselves toform a monolithic structure. Unlike other solution deposition methodsthat produce metal oxide powders on the surface that needhigh-temperature sintering, the method disclosed herein allows directproduction of a compact electrolyte layer at low temperatures, thisbeing a fundamental distinctive feature of the method.

The difference is attributed to the property of metal oxides depositedfrom carboxylates to have an amorphous structure during destruction. Anamorphous structure is a solid counterpart of liquids, and, by analogywith liquid electrolytes, it has the following advantages:

-   it provides for the greatest possible area of electrochemical    contact between the zirconium dioxide deposited electrolyte and the    electrode materials;-   it inherits the microroughnesses of the electrode surfaces,    including the surface of their open pores;-   it covers the open pores and microcracks on the surface of    electrodes.

Moreover, sequential transition from the liquid state of the organogelto a crystalline zirconium oxide structure through an intermediateamorphous state allows optimizing some useful properties of theelectrolyte, such as adhesion, internal stresses and diffusioninteraction at phase boundaries.

Stages of electrolyte formation on a microporous surface are as follows.

The first stage is deposition of the organogel onto the surface of theporous electrode 1 using any known method. During the synthesis of theinner nanoporous three-dimensional electrolyte layer 3, the depositionincludes impregnation of the surface pores 2 of the electrodes with theorganogel. The impregnation is performed by mechanical pressing of theorganogel into the porous surface of the electrode, e.g. with a paintroller, or by vacuum impregnation. Vacuum impregnation is preferablyused for small pore electrodes. For the production of the dense outerelectrolyte layer 4, the organogel is deposited by spraying or printing.

The second stage is destruction (decomposition) to produce anelectrolyte layer on the surface and remove the organic components in agaseous state.

The two above process stages can be unified by depositing the organogelonto the heated electrode surface by spraying or printing, provided thesurface temperature is sufficient for destruction.

The electrolyte layer can be synthesized using any process that causesdestruction of the organic part of the organogel, e.g. thermal,induction or infrared heating, or electron or laser beam impact orplasmachemical impact.

The simplest and cheapest method from the technological and economicalviewpoints is thermal destruction (pyrolysis). The destruction onsettemperature for the organogel is about 200° C. The process can beconducted under atmospheric pressure in air or in an inert or weaklyreducing gas atmosphere. The temperature and the gas atmospheredetermine the destruction rate and hence electrolyte properties.Stabilization of the intermediate amorphous state is preferablyperformed in an inert or weakly reducing gas atmosphere or usinghigh-rate destruction methods. The minimum electrolyte layer formationtime is 30 seconds.

For example, an electrolyte layer can be synthesized by heating theelectrode in an inert or weakly reducing gas atmosphere to within 800°C. and depositing the organogel onto the surface by spraying.High-temperature impregnation of the electrode surface pores occursimmediately upon the incidence of the organogel onto the surface. Duringdestruction, the organic part of the organogel decomposes to volatilecomponents, whereas the surface, including the surface pores, becomescovered with oxides that form the electrolyte layer. During the seconddeposition of the organogel the electrolyte layer forms on the surfaceof the first deposited layer. The density and properties of the outerelectrolyte layer are determined by the organogel composition andproperties.

Organogel can be deposited onto the cold electrode surface for furtherdestruction. For thermal destruction, the temperature should also bewithin 800° C.

The final synthesis of crystalline electrolyte from the already formedamorphous material layer implies final air heat treatment. Preferably,the heat treatment temperature should not exceed the working temperatureof the electrochemical device by more than 10-15%.

Organogel properties, such as particle composition, metal compositionand concentrations in the organic salt mixture, and the volume ratios ofthe particles and the carboxylate solution are chosen depending on thefinal electrolyte composition, thickness, substrate surface propertiesetc. These organogel properties allow controlling all the electrolyteparameters with due regard to the substrate surface properties.

The method allows producing electrolyte films on substrates of anymaterials, shapes and sizes.

The method is very efficient and cost-effective.

The method is easily adaptable to complete automation and conveyorfabrication setup.

The low electrolyte layer synthesis temperatures provide for yet anotherfundamental advantage in comparison with the other known methods. Thisadvantage is the absence of chemical interaction between the electrolyteand the electrode materials. This results in the absence of highlyelectrically resistant oxides on the phase boundary and hence providesfor a significant increase in current density and specific power of thefuel cell.

Below, the possibilities of the first electrode-electrolyte pairembodiment fabrication method and the organogel for this method will beillustrated with specific examples that do not limit the scope of thisinvention.

EXAMPLE 1

Organogel for the production of electrolyte of the ZrO₂—Y₂O₃ system,e.g., ZrO₂-3 mole % Y₂O₃ (3YZS being tetragonal partially stabilizedzirconium dioxide) and ZrO₂-8 mole % Y₂O₃ (8YSZ being cubic stabilizedzirconium dioxide).

Example 1.1

Zr and Y carboxylates with concentrations of 1.0 mole/l are produced byextraction of water salts of zirconium and yttrium to a mixture ofcarbonic acids with the general formula H(CH₂—CH₂)_(n)CR′R″—COOH, whereR′ is CH₃, R″ is C_(m)H_((m+1)) and m is from 2 to 6, with an averagemolecular weight of 140-250. The excess quantity of carbonic acids actas solvent. Zr and Y carboxylates are mixed in proportions correspondingto the stoichiometric composition ZrO₂-3 mole % Y₂O₃ or ZrO₂-8 mole %Y₂O₃.

The solutions of each carboxylate corresponding to the 3YSZ and 8YSZcompositions are mixed with 3-100 nm sized nanometric particles with the3YSZ and 8YSZ compositions, respectively. The volume ratio of thenanometric particles is 85% of the organic liquid volume.

Organogel according to Example 1.1 is used for the production of theinner nanoporous three-dimensional 3YSZ or 8YSZ composition electrolytelayer on metallic, metalloceramic or ceramic electrodes with pore sizesfrom 5 to 30 μm and penetration depth into the electrode of 10 to 60 μm,respectively.

Example 1.2

Solution of Zr and Y carboxylates with concentrations of 1.0 mole/l asin Example 1.1 corresponding to the 3YSZ and 8YSZ compositions isproduced.

The solutions of each carboxylate corresponding to the 3YSZ and 8YSZcompositions are mixed with 3-100 nm sized nanometric particles with the3YSZ and 8YSZ compositions, respectively. The volume ratio of thenanometric particles is 5 to 20% of the organic liquid volume.

Organogel according to Example 1.2 is used for the production of thedense outer 3YSZ or 8YSZ composition electrolyte layer on the surface ofthe inner nanoporous three-dimensional electrolyte layer based on dopedzirconium dioxide or on the surface of any other sublayer.

Example 1.3

Solution of Zr and Y carboxylates with concentrations of 0.05 mole/l asin Example 1.1 corresponding to the 3YSZ and 8YSZ compositions isproduced.

The solutions of each carboxylate corresponding to the 3YSZ and 8YSZcompositions are mixed with 3-100 nm sized nanometric particles with the3YSZ and 8YSZ compositions, respectively. The volume ratio of thenanometric particles is 20 to 50% of the organic liquid volume.

Organogel according to Example 1.3 is used for the production of theinner nanoporous three-dimensional 3YSZ or 8YSZ composition electrolytelayer on metallic, metalloceramic or ceramic electrodes with pore sizesfrom 1 to 5 μm and penetration depth into the electrode of 3 to 15 μm,respectively.

Example 1.4

Solution of Zr and Y carboxylates with concentrations of 0.05 mole/l asin Example 1.1 corresponding to the 3YSZ and 8YSZ compositions isproduced.

The solutions of each carboxylate corresponding to the 3YSZ and 8YSZcompositions are mixed with 3-100 nm sized nanometric particles with the3YSZ and 8YSZ compositions, respectively. The volume ratio of thenanometric particles is 1 to 10% of the organic liquid volume.

Organogel according to Example 1.4 is used for the production of thedense outer 3YSZ or 8YSZ composition electrolyte layer on the surface ofthe inner nanoporous three-dimensional electrolyte layer based on dopedzirconium dioxide or on the surface of any other sublayer.

EXAMPLE 2

Organogel for the production of electrolyte of the ZrO₂—Sc₂O₃ andZrO₂—Sc₂O₃—Al₂O₃ systems.

Example 2.1

Zr, Sc and Al carboxylates with concentrations of 0.05 to 1.0 mole/l areproduced by extraction of water salts of zirconium, scandium andaluminum to a mixture of carbonic acids with the general formulaH(CH₂—CH₂)_(n)CR′R″—COOH, where R′ is CH₃, R″ is C_(m)H_((m+1)) and m isfrom 2 to 6, with an average molecular weight of 140-250. The excessquantity of carbonic acids act as solvent. Zr, Sc and Al carboxylatesare mixed in proportions corresponding to the stoichiometric compositionZrO₂—Sc₂O₃ or ZrO₂—Sc₂O₃—Al₂O₃.

The solutions of each carboxylate corresponding to the ZrO₂—Sc₂O₃ orZrO₂—Sc₂O₃—Al2O3 system compositions are mixed with 3-100 nm sizednanometric particles with the ZrO₂—Sc₂O₃ or ZrO₂—Sc₂O₃—Al2O3 systemcompositions, respectively.

The volume ratio of the nanometric particles is 40 to 60% of the organicliquid volume.

Organogel according to Example 2.1 is used for the production of theinner nanoporous three-dimensional ZrO₂—Sc₂O₃ or ZrO₂—Sc₂O₃—Al2O3 systemcomposition electrolyte layer on metallic, metalloceramic or ceramicelectrodes with pore sizes from 3 to 10 μm and penetration depth intothe electrode of 6 to 20 μm, respectively.

Example 2.2

Zr, Sc and Al carboxylate solutions with concentrations of 0.05 to 1.0mole/l as in Example 2.1. corresponding to the stoichiometriccomposition of the ZrO₂—Sc₂O₃ or ZrO₂—Sc₂O₃—Al2O3 system are produced.

The solutions of each carboxylate corresponding to the ZrO₂—Sc₂O₃ orZrO₂—Sc₂O₃—Al2O3 system compositions are mixed with 3-100 nm sizednanometric particles with the ZrO₂—Sc₂O₃ or ZrO₂—Sc₂O₃—Al2O3 systemcompositions, respectively.

The volume ratio of the nanometric particles is 1 to 20% of the organicliquid volume.

Organogel according to Example 2.2 is used for the production of thedense outer electrolyte layer with the ZrO₂—Sc₂O₃ or ZrO₂—Sc₂O₃—Al2O3system composition.

EXAMPLE 3

Organogel for the production of electrolyte of the (Zr,Y,Tb)O₂ systemhaving a combined type of conductivity, e.g. Zr_(1−x−y)Y_(x)Tb_(y)O_(2−z), where x=0.12-0.2 and y=0.15-0.2.

Example 3.1

Zr, Tb and Y carboxylates with concentrations of 1.0 mole/l are producedby extraction of water salts of zirconium, terbium and yttrium to amixture of carbonic acids with the general formulaH(CH₂—CH₂)_(n)CR′R″—COOH, where R′ is CH₃, R″ is C_(m)H_((m+1)) and m isfrom 2 to 6, with an average molecular weight of 140-250. The excessquantity of carbonic acids act as solvent. Zr, Tb and Y carboxylates aremixed in proportions corresponding to the stoichiometric compositionZr_(1−x−y) Y_(x)Tb_(y)O_(2−z), where x=0.12-0.2 and y=0.15-0.2.

The solution is mixed with 3-100 nm sized nanometric particles with theZr_(1−x−y) Y_(x)Tb_(y)O_(2−z) composition. The volume ratio of thenanometric particles is 50 to 85% of the organic liquid volume.

Organogel according to Example 3.1 is preferably used for the productionof the inner nanoporous three-dimensional Zr_(1−x−y) Y_(x)Tb_(y)O_(2−z)electrolyte layer on metallic or ceramic electrodes with pore sizes from5 to 30 μm and penetration depth into the electrode of 10 to 60 μm,respectively.

Example 3.2

Zr, Tb and Y carboxylates with concentrations of 0.05 to 0.5 mole/l areproduced as in Example 3.1. Zr, Tb and Y carboxylates are mixed inproportions corresponding to the stoichiometric composition Zr_(1−x−y)Y_(x)Tb_(y)O_(2−z), where x=0.12-0.2 and y=0.15-0.2.

The solution is mixed with 3-100 nm sized nanometric particles with theZr_(1−x−y) Y_(x)Tb_(y)O_(2−z) composition. The volume ratio of thenanometric particles is 20 to 50% of the organic liquid volume.

Organogel according to Example 3.2 is preferably used for the productionof the inner nanoporous three-dimensional Zr_(1−x−y) Y_(x)Tb_(y)O_(2−z)electrolyte layer on metallic or ceramic electrodes with pore sizes from1 to 7 μm and penetration depth into the electrode of 3 to 15 μm,respectively.

EXAMPLE 4

Organogel for the production of electrolyte of the (Zr,Y)O₂—TiO₂ systemhaving a combined type of conductivity, e.g. ZrO₂-12 mole % Y₂O₃-20 mole% TiO₂.

Zr, Ti and Y carboxylates with concentrations of 0.05 to 1.0 mole/l areproduced by extraction of water salts of zirconium, titanium and yttriumto a mixture of carbonic acids with the general formulaH(CH₂—CH₂)_(n)CR′R″—COOH, where R′ is CH₃, R″ is C_(m)H_((m+1)) and m isfrom 2 to 6, with an average molecular weight of 140-250. The excessquantity of carbonic acids act as solvent. Zr, Ti and Y carboxylates aremixed in proportions corresponding to the stoichiometric compositionZrO₂-12 mole % Y₂O₃-20 mole % TiO₂.

The solution is mixed with 3-100 nm sized nanometric particles with theZrO₂-12 mole % Y₂O₃-20 mole % TiO₂ composition. The volume ratio of thenanometric particles is 20 to 85% of the organic liquid volume.

Organogel according to Example 4 is preferably used for the productionof the inner nanoporous three-dimensional ZrO₂-12 mole % Y₂O₃-20 mole %TiO2 electrolyte layer with pore sizes of above 1 μm.

EXAMPLE 5

Method of fabricating an electrode-electrolyte pair comprising amicroporous electrode and a two-layered electrolyte based on zirconiumdioxide.

The electrode materials for this example can be as follows:

-   -   ceramic cathode, e.g. of the perovskites group of the        manganites, cobaltites, nickelites, chromites etc. family;    -   metallic cathode made from, e.g. ferritic steel with a        functional cathodic sublayer;    -   metalloceramic anode, e.g. of the Ni-8YSZ, Co-8YSZ etc. system;    -   metallic anode made from foam metal or volume mesh consisting of        nickel, cobalt or their alloys.

The electrode shape is flat or pipe-like. The electrode may havewell-developed surface roughness, porosity of 30 to 70% and pore size of1 to 30 μm.

Example 5.1

Method of fabricating a pair of a La_(0.8) Sr_(0.2) Mn O₃ cathode and atwo-layered 8YSZ based electrolyte.

The cathode has a porosity of 30% and an average pore size of 5 μm.

The electrolyte is produced by thermal destruction. The deposition isperformed in at least two stages.

At the first stage, the inner nanoporous three-dimensional 8YSZelectrolyte layer is produced, primarily in the electrode surface pores.The function of the inner 8YSZ electrolyte layer is as follows:

-   1. transformation of large cathode surface pores to a nanoporous    material corresponding to the 8YSZ electrolyte composition;-   2. relieving of the internal and thermal stresses at the phase    boundary of the two contacting materials and in the electrode    material layer towards the electrolyte;-   3. elimination of the negative effect of surface stress    concentrators in the electrode material;-   4. maximizing the electrochemical contact area with the electrolyte    at the electrolyte side.

The inner 8YSZ electrolyte layer is obtained using the organogelaccording to Examples 1.1 or 1.3.

The organogel is deposited onto the cold surface with a roller bypressing it into the electrode surface pores or by one-side vacuumimpregnation of the porous electrode. Destruction is performed byheating the electrode to 500-800° C. in an argon atmosphere or in anargon and hydrogen mixture at reference pressure. Destruction produces,on the heated electrode surface, a partially amorphous three-dimensionallayer of nanoporous 8YSZ electrolyte penetrating into the electrodepores to 10-15 μm. Electrolyte properties are stabilized bycrystallization annealing at 800-1100° C. exceeding the workingtemperature of the electrochemical device by at least 15%, theelectrolyte grain size being 30-1000 nm.

At the second stage, a dense two-dimensional 8YSZ electrolyte layer isproduced on the surface of the preliminarily synthesized 8YSZelectrolyte sublayer.

This is performed using the organogel according to Examples 1.2 or 1.4.The organogel is deposited onto the cold functional sublayer surfacewith subsequent heating to 500-800° C. in an argon atmosphere or in anargon and hydrogen mixture or onto the sublayer surface heated to500-800° C. in a similar atmosphere. The final treatment is in air at800-1100° C. exceeding the working temperature of the electrochemicaldevice by at least 15%. As a result, a dense, defect- and crack-freetwo-dimensional 8YSZ electrolyte layer with a grain size of 30-1000 nmforms on the sublayer surface. The thickness of this latter layer is3-10 μm.

Organogel according to Example 1.4 can be deposited onto the sublayersurface heated to 200-500° C. in air or in an inert atmosphere.Destruction produces dense, defect- and crack-free two-dimensional 8YSZelectrolyte layer on the sublayer surface. The final treatment is in airat 800-1100° C. exceeding the working temperature of the electrochemicaldevice by at least 15%. As a result, a dense, defect- and crack-freetwo-dimensional 8YSZ electrolyte layer with a grain size of 30-1000 nmforms on the sublayer surface. The thickness of this latter layer is 1-5μm.

The electrolyte produced as above was a continuous layer part of which,i.e. the three-dimensional nanoporous electrolyte, penetrated into theporous electrode structure, and the other part, i.e. the densetwo-dimensional layer was uniformly distributed over the surface andinherited its roughness pattern.

Example 5.2

Method of fabricating a pair of a La_(0.8) Sr_(0.2) Mn O₃ cathode and atwo-layered electrolyte based on zirconium dioxide of differentcompositions.

The cathode has a porosity of 30% and an average pore size of 5 μm.

The electrolyte is produced by thermal destruction. The deposition isperformed in at least two stages.

At the first stage, the inner nanoporous three-dimensional Zr_(1−x−y)Y_(x)Tb_(y)O_(2−z) electrolyte layer having a combined ionic andelectronic p-type of conductivity is produced. The function of the innerZr_(1−x−y) Y_(x)Tb_(y)O_(2−z) electrolyte layer is as follows:

-   1. transformation of large cathode surface pores to a nanoporous    material corresponding to the Zr_(1−x−y) Y_(x)Tb_(y)O_(2−z)    electrolyte composition;-   2. relieving of the internal and thermal stresses at the phase    boundary of the two contacting materials and in the electrode    material layer towards the electrolyte;-   3. elimination of the negative effect of surface stress    concentrators in the electrode material;-   4. maximizing the electrochemical contact area with the electrolyte    at the electrode side;-   5. maximizing the electrochemical contact area with the electrolyte    at the electrolyte side;-   6. minimization of the cathode resistance.

The inner Zr_(1−x−y) Y_(x)Tb_(y)O_(2−z) electrolyte layer is producedusing the organogel according to Example 3.1.

The inner layer production method is as in Example 5.1.

At the second stage, a dense two-dimensional Zr_(1−x−y)Y_(x)Tb_(y)O_(2−z) electrolyte layer is produced on the surface of thepreliminarily synthesized Zr_(1−x−y) Y_(x)Tb_(y)O_(2−z) electrolytesublayer.

This is performed using the organogel according to Example 2.2. Thedense outer layer production method is as in Example 5.1.

The electrolyte produced as above was a continuous layer part of which,i.e. the three-dimensional nanoporous electrolyte of the Zr_(1−x−y)Y_(x)Tb_(y)O_(2−z) composition, penetrated into the porous electrodestructure, and the surface layer, i.e. the dense two-dimensionalZrO₂—Sc₂ layer was uniformly distributed over the surface and inheritedits roughness pattern.

Example 5.3

Method of fabricating a pair of a 50% NiO-50% 8YSZ anode and atwo-layered electrolyte based on zirconium dioxide of differentcompositions.

The cathode has a porosity of 30% and an average pore size of 3 μm.

The electrolyte is produced by thermal destruction. The deposition isperformed in at least two stages.

At the first stage, the inner nanoporous three-dimensional ZrO₂-12 mole% Y₂O₃-20 mole % TiO₂ electrolyte layer having a combined ionic andelectronic p-type of conductivity is produced. The function of the innerZrO₂-12 mole % Y₂O₃-20 mole % TiO₂ electrolyte layer is as follows:

-   1. transformation of large cathode surface pores to a nanoporous    material corresponding to the ZrO₂-12 mole % Y₂O₃-20 mole % TiO₂    electrolyte composition;-   2. relieving of the internal and thermal stresses at the phase    boundary of the two contacting materials and in the anode material    layer towards the electrolyte;-   3. elimination of the negative effect of surface stress    concentrators in the anode material;-   4. maximizing the electrochemical contact area with the electrolyte    at the anode side;-   5. maximizing the electrochemical contact area between the gaseous    fuel, the anode material and the electrolyte;-   6. minimization of the anode resistance.

The inner ZrO₂-12 mole % Y₂O₃-20 mole % TiO₂ electrolyte layer isproduced using the organogel according to Example 4.

The inner layer production method is as in Example 5.1.

At the second stage, a dense two-dimensional 8YSZ or ZrSc_(0.15)O₂electrolyte layer is produced on the surface of the preliminarilysynthesized ZrO₂-12 mole % Y₂O₃-20 mole % TiO₂ electrolyte sublayer.

This is performed using the organogel according to Examples 1.4 or 2.2.The dense outer layer production method is as in Example 5.1.

The electrolyte produced as above was a continuous layer part of which,i.e. the three-dimensional nanoporous electrolyte of the ZrO₂-12 mole %Y₂O₃-20 mole % TiO₂ composition with a combined type of conductivity,penetrated into the porous electrode structure to 6-8 μm, and thesurface layer, i.e. the dense two-dimensional 8YSZ or ZrSc_(0.15)O₂layer was uniformly distributed over the surface and inherited itsroughness pattern.

Example 5.4

Method of fabricating a pair of a (nickel, cobalt or their alloy) anodeand a two-layered electrolyte based on zirconium dioxide of different orsimilar compositions.

The metallic anode is a foam metal or a volume mesh and has a porosityof 30-60% and an average pore size of 10-50 μm.

The electrolyte is produced by thermal destruction. The deposition isperformed in at least two stages.

At the first stage, the inner nanoporous three-dimensional ZrO₂-12 mole% Y₂O₃-20 mole % TiO₂ electrolyte layer having a combined ionic andelectronic n-type of conductivity, as in Example, 5.3, or a 8YSZ layerhaving an ionic type of conductivity, as in Example 5.1, is produced.The function of the inner electrolyte layer is as in Example 5.3 orExample 5.1.

The inner layer production method is as in Example 5.1 or Example 5.3.

At the second stage, a dense two-dimensional 8YSZ electrolyte layer isproduced on the surface of the preliminarily synthesized sublayer.

This is performed using the organogel according to Example 1.4. Thedense outer layer production method is as in Example 5.1.

The electrolyte produced as above was a continuous layer part of which,i.e. the three-dimensional nanoporous electrolyte of the ZrO₂-12 mole %Y₂O₃-20 mole % TiO₂ composition with a combined type of conductivity or8YSZ with an ionic type of conductivity, penetrated into the porouselectrode structure to 20-100 μm, and the surface layer, i.e. the densetwo-dimensional 8YSZ layer was uniformly distributed over the surfaceand inherited its roughness pattern.

The second embodiment of the electrode-electrolyte pair suggested anddisclosed herein (FIG. 2) is fabricated using the second suggestedfabrication method.

The electrolyte production method is based on destruction(decomposition) of the organic component of the organic solution ofzirconium and stabilizing metal salts deposited onto the electrodesurface. The organic salts are carboxylates of zirconium, calcium,magnesium, yttrium, scandium and aluminum in a mixture of α-branchingcarbonic acids with the general formula H(CH₂—CH₂)_(n)CR′R″—COOH, whereR′ is CH₃, R″ is C_(m)H_((m+1)) and m is from 2 to 6, with an averagemolecular weight of 140-250. The organic salt solvent is any carbonicacids, e.g. toluene, octanol or other organic solvent.

As a result of the destruction, an amorphous oxide layer forms on thesurface, the composition of which corresponds to that of stabilizedzirconium oxide. Unlike other solution deposition methods that producemetal oxide powders on the surface that need high-temperature sintering,the method disclosed herein allows direct production of a dense anddefect-free electrolyte layer at low temperatures, this being afundamental distinctive feature of the method.

The first stage is deposition of the solution onto the surface of theporous electrode 1 using any known method, preferably, spraying orprinting. Due to the high liquidity and wetting capacity of thesolution, impregnation of the surface pores 6 sized less than 1 μm to adepth of 1-5 μm occur automatically and does not requires any specialmethods.

The second stage is destruction (decomposition) to produce a denseelectrolyte layer 7 on the surface and remove the organic components ina gaseous state.

The two above process stages can be unified by depositing the solutiononto the heated electrode surface 5, provided the surface temperature issufficient for destruction.

The electrolyte layer can be synthesized using any process that causesdestruction of the organic part of the solution, e.g. thermal, inductionor infrared heating, or electron or laser beam impact or plasmachemicalimpact.

The simplest and cheapest method from the technological and economicalviewpoints is thermal destruction (pyrolysis). The destructiontemperature is within 800° C., the preferable thermal destructiontemperature range being 200-600° C. The process can be conducted underatmospheric pressure in air or in an inert or weakly reducing gasatmosphere. The temperature and the gas atmosphere determine thedestruction rate and hence electrolyte properties. Stabilization of theintermediate amorphous state is preferably performed in an inert orweakly reducing gas atmosphere or using high-rate destruction methods.The minimum electrolyte layer formation time is 30 seconds. Destructionin air increases the oxide layer formation rate, the minimum electrolytelayer formation time in this case being 5-10 seconds.

The method of solution deposition onto the heated surface withsimultaneous destruction is more rapid and efficient, but it leads toelevated stresses in the electrolyte layer and at the phase boundary.

The method of solution deposition onto the cold surface with subsequentdestruction is less efficient, but it reduces the stress level in thelayer and produces a layer that is more uniform across its thicknesswhich is important, e.g. for the fabrication of an electrode-electrolytepair having a high surface area. Moreover, this method is preferable formultiple electrolyte layer deposition to exclude electrolyte layerrejects as multiple layer deposition heals possible defects.

The final synthesis of crystalline electrolyte from the already formedamorphous material layer implies final air heat treatment. Preferably,the heat treatment temperature should not exceed the working temperatureof the electrochemical device by more than 10-15%.

The distinctive feature of this method is the possibility of producingthin defect-free zirconium dioxide electrolyte layers composing anelectrode-electrolyte layer with two-layered electrolyte, e.g.,CeO₂/ZrO₂ BiO₂/ZrO₂ or La(Sr)Ga(Mg)O₃/ZrO₂.

The choice of the solution deposition and destruction method and gasatmosphere composition provide for the high adaptability of the methodand allow producing high-quality electrode-electrolyte pairs with dueregard to the properties and parameters of the composing materials.

Below, the possibilities of the second electrode-electrolyte pairfabrication method will be illustrated with specific examples that donot limit the scope of this invention (FIG. 2).

EXAMPLE 6

Method of fabricating an electrode-electrolyte pair comprising ananoporous electrode (sublayer) and a dense thin electrolyte based onzirconium dioxide.

The electrode or electrode sublayer materials for this example can be asfollows:

-   -   ceramic cathode, e.g. of the perovskites group of the        manganites, cobaltites, nickelites, chromites etc. family;    -   metallic cathode made from, e.g. ferritic steel with a        functional cathodic sublayer;    -   metalloceramic anode, e.g. of the Ni-8YSZ, Co-8YSZ etc. system;    -   metallic anode made from foam metal or volume mesh consisting of        nickel, cobalt or their alloys with an anode sublayer;    -   electrode with other electrolyte on the surface.

The electrode shape is flat or pipe-like. The electrode (sublayer) mayhave well-developed surface roughness, porosity of 0 to 35% and a poresize of less than 1 μm.

Example 6.1

Method of fabricating a pair of a 50% NiO-50% 3YSZ anode with a 50%NiO-50% 3YSZ sublayer and a dense 3YSZ electrolyte layer.

The cathode has a porosity of 35% and an average pore size of less than1 μm.

The sublayer thickness is 10 μm.

The electrolyte is produced by thermal destruction. The deposition isperformed in at least one stage.

The dense 3YSZ electrolyte layer is produced using a solution of amixture of zirconium and yttrium carboxylates in toluene with a totalzirconium and yttrium concentration of 0.5 mole/l, their molar ratiobeing 94 mole % Zr-6 mole % Y.

The solution is deposited onto the cold surface by printing, followingwhich the anode is air heated at atmospheric pressure to 300° C. Underthese conditions, the anode sublayer surface pores are impregnated to adepth of 3-5 μm. Destruction of the organic part of the solutionproduces a dense amorphous surface 3YSZ layer penetrating into thesublayer to 3-5 μm, the layer thickness on the surface being less than 1μm. If the 3YSZ layer thickness should be increased, the deposition anddestruction cycle is repeated.

The final annealing at 1000° C. produces tetragonal zirconium dioxidewith a density of 99.8% of the theoretical one and a grain size of 30-40nm.

Example 6.2

Method of fabricating a pair of a metallic anode with a nanoporousscandium stabilized 50% NiO-50% ZrO₂ sublayer and a dense scandiumstabilized zirconium dioxide (ScSZ) electrolyte layer.

The cathode has a porosity of 30% and an average pore size of less than1 μm.

The sublayer thickness is 50 μm.

The electrolyte is produced by solution deposition with simultaneousthermal destruction.

The dense ScSZ electrolyte sublayer is produced using a solution of amixture of zirconium and scandium carboxylates with an excessivequantity of carbonic acids with the general formulaH(CH₂—CH₂)_(n)CR′R″—COOH, where R′ is CH₃, R″ is C_(m)H_((m+1)) and m isfrom 2 to 6, with an average molecular weight of 140-250, the totalzirconium and scandium concentration being 1 mole/l, and their ratiobeing stoichiometric.

The solution is deposited onto the surface heated to 400° C. by multipleprinting at atmospheric pressure in an argon atmosphere. Under theseconditions (during the first deposition cycle), the anode sublayersurface pores are impregnated to a depth of 1-2 μm with further increaseof the ScSZ electrolyte layer. Each cycle is 1 minute long.

This technology produces a dense amorphous surface ScSZ layerpenetrating into the sublayer to 1-2 μm, the layer thickness on thesurface being 1 to 15 μm.

The final annealing at 800° C. produces cubic zirconium dioxide with adensity of 99.5% of the theoretical one and a grain size of 10-15 nm.

Example 6.3

Method of fabricating a pair of a La_(0.6) Sr_(0.4)CoO₃ cathode with aLa_(0.6) Sr_(0.4)CoO₃ sublayer and a dense 8YSZ electrolyte layer.

The cathode has a porosity of 35% and an average pore size of less than1 μm.

The sublayer thickness is 5 μm.

The electrolyte is produced by thermal destruction. The deposition isperformed in at least one stage.

The dense 8YSZ electrolyte layer is produced using a solution of amixture of zirconium and yttrium carboxylates in toluene with a totalzirconium and yttrium concentration of 0.1 mole/l, their molar ratiobeing 84 mole % Zr-16 mole % Y.

The solution is deposited onto the cold surface by spraying, followingwhich the cathode is air heated at atmospheric pressure to 300° C. Underthese conditions, the cathode sublayer surface pores are impregnated toa depth of up to 5 μm. Destruction of the organic part of the solutionproduces a dense amorphous surface 8YSZ layer penetrating into thesublayer to the full sublayer depth, the layer thickness on the surfacebeing 0.3 μm. If the 8YSZ layer thickness should be increased, thedeposition and destruction cycle is repeated.

The final annealing at 600° C. produces tetragonal zirconium dioxidewith a density of 99.8% of the theoretical one and a grain size of 3-8nm.

1. Electrode-electrolyte pair comprising a microporous electrode to thesurface of which is deposited a multilayered solid electrolyte based onzirconium dioxide with stabilizing additions, the solid electrolyteconsisting of the inner nanoporous three-dimensional solid electrolytelayer with a grain size of within 1000 nm which fills, at leastpartially, the surface pores of the microporous electrode to a depth of5-50 μm, and a dense outer electrode layer with a grain size of within1000 nm located on the surface of said inner layer. 2.Electrode-electrolyte pair according to claim 1, wherein said inner andouter electrolyte layers have similar or different compositions. 3.Electrode-electrolyte pair according to claim 1, wherein said innerelectrolyte layer has a combined amorphous and nanocrystallinestructure.
 4. Electrode-electrolyte pair according to claim 1, whereinsaid outer electrolyte layer has an amorphous structure. 5.Electrode-electrolyte pair according to claim 1, wherein saidstabilizing additions are magnesium and/or calcium and/or yttrium and/orscandium and/or aluminum and/or rare earth metals and/or titanium. 6.Electrode-electrolyte pair according to claim 1, wherein said electrodeis made of a microporous ceramic or metallic or metalloceramic materialwith pore sizes of above 1 μm.
 7. Electrode-electrolyte pair accordingto claim 1, wherein said electrode is a cathode or anode of flat orpipe-like shape.
 8. Electrode-electrolyte pair according to claim 7,wherein said anode is made of a porous metallic material consisting ofnickel and/or cobalt and/or their alloys.
 9. Electrode-electrolyte pairaccording to claim 7, wherein said anode is made of a volume mesh or afoam material.
 10. Electrode-electrolyte pair fabrication methodcomprising the formation, on the microporous electrode surface, of apartially electrode-penetrating multilayered solid electrolyte based onzirconium dioxide with stabilizing additions, to which end themicroporous electrode surface is initially impregnated with organogelconsisting of particles of zirconium dioxide with stabilizing additionsand an organic solution containing organic salts of zirconium and thestabilizing metals, and destruction of the organogel organic part thatleads to the chemical deposition of the inner nanoporousthree-dimensional solid electrolyte layer on the electrode surface,following which the inner organogel layer is deposited onto the surface,said layer consisting of nanosized particles of zirconium dioxide withstabilizing additions and an organic solution containing organic saltsof zirconium and the stabilizing metals, and destruction of theorganogel organic part that leads to the chemical deposition of thedense outer layer of the multilayered electrolyte onto the inner layersurface.
 11. Method according to claim 10, wherein said inner and outerelectrolyte layers are produced using organogel of similar or differentcompositions.
 12. Method according to claim 10, wherein said stabilizingadditions are magnesium and/or calcium and/or yttrium and/or scandiumand/or aluminum and/or rare earth metals and/or titanium.
 13. Methodaccording to claim 10, wherein the impregnation of said porous electrodesurface with organogel is performed in vacuum of by mechanical pressingthe organogel into the porous electrode surface.
 14. Method according toclaim 10, wherein said destruction is performed by high-energy impactthat causes the decomposition of the organic part of the organogel, e.g.thermal, induction or infrared heating, or electron or laser beam impactor plasmachemical impact.
 15. Method according to claim 14, wherein saidorganogel destruction is performed with high-rate pyrolysis attemperatures within 800° C. in an oxidizing, inert or weakly reducinggas atmosphere.
 16. Method according to claim 10, wherein organogelorganic part destruction is performed simultaneously or sequentiallywith the impregnation or organogel deposition onto the inner layersurface.
 17. Method according to claim 16, wherein during organogelimpregnation of the electrode or organogel deposition to the inner layersurface with simultaneous destruction, the organogel is deposited to thesurface to be coated by spraying or printing.
 18. Method according toclaim 14, wherein during organogel impregnation of the electrode ororganogel deposition to the inner layer surface with subsequentdestruction, the organogel is deposited to the cold surface of theelectrode or the inner layer with subsequent high-rate heating of theelectrode.
 19. Method according to claim 10, wherein organogelimpregnation of the electrode or organogel deposition to the inner layersurface and organogel destruction are performed in one or multiplestages.
 20. Organogel used for the fabrication of theelectrode-electrolyte pair contains nanosized particles of zirconiumdioxide with stabilizing additions and an organic solution containingorganic salts of zirconium and the stabilizing metals, a mixture ofbranching carbonic acids with the general formulaH(CH₂—CH₂)_(n)CR′R″—COOH, where R′ is CH₃, R″ is C_(m)H_((m+1)) and m isfrom 2 to 6, with an average molecular weight of 140-250.
 21. Organogelaccording to claim 20, wherein said stabilizing additions are magnesiumand/or calcium and/or yttrium and/or scandium and/or aluminum and/orrare earth metals and/or titanium.
 22. Organogel according to claim 20,wherein said organic solvent is carbonic acid and/or any organic solventof carbonic acid metal salts.
 23. Organogel according to claim 20,wherein said organogel contains nanosized particles 3 to 100 nm in size.24. Organogel according to claim 20, wherein the concentration ofstabilizing additions in zirconium and metal salts in the organogel isselected at 0.05 to 1 mole/l in a ratio corresponding to the electrolytestoichiometric composition.
 25. Organogel according to claim 20, whereinthe volume ratio of the nanosized particles in the organogel is within85%.
 26. Electrode-electrolyte pair comprising a nanoporous electrode tothe surface of which is deposited a layer or dense three-dimensionedelectrolyte based on zirconium dioxide with stabilizing additions thegrain size of which is within 1000 nm, the electrolyte filling thesurface pores of the nanoporous electrode to a depth of 1-5 μm. 27.Electrode-electrolyte pair according to claim 26, wherein saidelectrolyte has an amorphous structure.
 28. Electrode-electrolyte pairaccording to claim 26, wherein said stabilizing additions are magnesiumand/or calcium and/or yttrium and/or scandium and/or aluminum and/orrare earth metals and/or titanium.
 29. Electrode-electrolyte pairaccording to claim 26, wherein said electrode is in a microporousceramic or metallic or metalloceramic material with pore sizes, at leastnear the surface, of within 1 μm.
 30. Electrode-electrolyte pairaccording to claim 26, wherein said electrode is an anode or cathodewith a flat or pipe-like shape.
 31. Electrode-electrolyte pair accordingto claim 30, wherein said anode is made of a porous metallic materialconsisting of nickel and/or cobalt and/or their alloys. 32.Electrode-electrolyte pair fabrication method comprising the formation,on the microporous electrode surface, of a dense three-dimensional solidelectrolyte layer based on zirconium dioxide with stabilizing additions,for which end the nanoporous electrode surface is initially impregnatedwith an organic solution containing organic salts of zirconium and thestabilizing metals, a mixture of α-branching carbonic acids with thegeneral formula H(CH₂—CH₂)_(n)CR′R″—COOH, where R′ is CH₃, R″ isC_(m)H_((m+1)) and m is from 2 to 6, with an average molecular weight of140-250, and destruction of the organogel organic part that leads to thechemical deposition of the solid electrolyte on the electrode surface.33. Method according to claim 32, wherein said stabilizing additions aremagnesium and/or calcium and/or yttrium and/or scandium and/or aluminumand/or rare earth metals and/or titanium.
 34. Method according to claim32, wherein said organic solvent is carbonic acid or toluene or octanolor any organic solvent of carbonic acid metal salts.
 35. Methodaccording to claim 32, wherein said destruction is performed byhigh-energy impact that causes the decomposition of the organic part ofthe organogel, e.g. thermal, induction or infrared heating, or electronor laser beam impact or plasmachemical impact.
 36. Method according toclaim 35, wherein said organogel destruction is performed with high-ratepyrolysis at temperatures within 800° C. in an oxidizing, inert orweakly reducing gas atmosphere.
 37. Method according to claim 32,wherein said organogel organic part destruction is performedsimultaneously or sequentially with impregnation.
 38. Method accordingto claim 37, wherein during electrode impregnation with simultaneousdestruction, the solution is deposited to the surface to be coated byspraying or printing.
 39. Method according to claim 37, wherein duringelectrode impregnation with subsequent destruction, the solution isdeposited to the cold surface of the electrode with subsequent high-rateheating of the electrode.
 40. Method according to claim 32, wherein theconcentration of stabilizing additions is selected at 0.05 to 1 mole/lin a ratio corresponding to the electrolyte stoichiometric composition.41. Organogel according to claim 32, wherein said solution is depositedonto the electrode surface and destruction in one or multiple stages.